A UIRefreshControl object provides a standard control that can be used to
initiate the refreshing of a table view’s contents. When pulled, a little
wheel starts spinning at the top, until the refresh has completed. At that
time, the wheel disappears, and the view bounces back into place. In this
tutorial we will add a refresh control to a table view. When the controll
is pulled the sorting order of the rows will be inversed. This tutorial is
built with iOS 8.1 and Xcode 6.1.